Snow throwers throw up snow about 6 - 10 feet up, wasting lot of energy. I-Shovel efficiently pushes snow when it's still fresh and light in relatively short cycles. The computer algorithm controlling the robot closely mimics the shoveling process a human usually does with a manual shovel.
Availability: unknown. The company is looking for partnerships. A Japanese invention, the Yuki-taro snow-munching machine is the result of nearly seven years of work by researchers "who set out to design an environmentally-friendly robot that can operate by itself and support the elderly." (Not to mention the too-busy-infirm-lazy-to-shovel.) No word on what powers the Yuki-taro. But the green lining is that it "eats up snow and poops ice blocks" which can be stored and used for refrigeration or cooling in warmer temps. Availability: unknown. At least three years away.
The greenest snow-clearing device I have found that isn't a shovel isn't a robot either. It's called the Wovel and it is commercially available: It's a snow mover with an 18th-century profile and a 21st-century environmental sensibility. My brother, who uses it to clear his 120-foot driveway, says "While the snow throwers down the road whine and spew fumes, I can feel a little smug about my eco-peaceful, back-friendly workout. It's Woverly."
The Wovel in action:
The i-Shovel in action: